Interlocks for folding box panels



Dec. 2, 1969 c. J. PIERCE, JR 3,481,525

INTERLOCKS FOR FOLDING BOX PANELS Filed Aug 2, 1968 ll Sheets-Sheet l INVENTOR. C/resfer J Pierce, Jr:

1969 c. J. PIERCE, JR 3, 8

INTERLOCKS FOR FOLDING BOX PANELS Filed Aug 2, 1968 ll Sheets-Sheet 2 INVENTOR. Cfiesler J. Pzerce; Jr:

M4 ATTORNEY Dec. 2, 1969 c. J. PIERCE, JR

INTERLOCKS FOR FOLDING BOX PANELS Filed Aug 2, 1968 ll Sheets-Sheet 5 INVENTOR. Chesfer J. Pierce, Jr.

4M ATTOR/VEV Dec. 2, 1969 c. J. PIERCE, JR I 3,481,525

INTERLOCKS FOR FOLDING BOX PANELS Filed Aug 2, 1968 ll Sheets-Sheet 4 INVENTOR. Chesfer .1 Pierce, Jr.

ATTORNEY Dec. 2, 1969 c. J. PIERCE, JR 3,

INTERLOCKS FOR FOLDING BOX PANELS ll Sheets-Sheet 5 Filed Aug 2, 1968 A 64/: ATTORNEY Dec. 2, 1969 c. J. PIERCE, JR

INTERLOCKS FOR FOLDING BOX PANELS l1 Sheets-Sheet 6 Filed Aug 2, 1968 & mi

INVENTOR. Chesfer J. Pierce, Jn

A TTORNEY Dec. 2, 1969 C. J. PIERCE, JR

INTERLOCKS FOR FOLDING BOX PANELS l1 Sheets-Sheet 7 Filed Aug 2, 1968 Q mi , INVENTOR. C/76Sfef J. Pierce, Jr.

Dec. 2, 1969 c. J. PIERCE, JR 3,

INTERLOCKS FOR FOLDING BOX PANELS Filed Aug 2, 1968 11 Sheets-Sheet a I NVENTOR. Cfiesfer J. Pierce, Jr.

YIBY

0 M ,4 TTORNEV Dec. 2, 1969 c. J. PIERCE, JR 3,481,525

INTERLOCKS FOR FOLDING BOX PANELS INVENTOR. C/7esfer J Pierce, J/t- Dec. 2, 1969 c. J. PIERCE, JR 3,481,525

INTERLOCKS FOR FOLDING BOX PANELS Filed Aug 2, 1968 11 Sheets-Sheet 10 x 204? 2044 i r 2043 w 23 i i K i INVENTOR. CheS/er J. Pierce, Jr.

U ATTORMFY Dec. 2, 1969 c. J. PIERCOE, JR 3,481,525

INTERLOCKS FOR FOLDING BOX PANELS Filed Aug 2, 1968 11 Sheets-Sheet 11 I /739 /74/ I732 [737 x /74/ //743 I738 73 j I 2 I 1732 I742 INVENTOR. C'hesfer J. Pierce, Jr,

U, ATTORNEY United States Patent INTERLOCKS FOR FOLDING BOX PANELS Chester J. Pierce, Jr., Palo Alto, Calif., assignor to Kllklok Corporation, New York, N.Y., a corporation of Delaware Filed Aug. 2, 1968, Ser. No. 749,647 Int. Cl. B65d 5/26 U.S. Cl. 229-35 24 Claims ABSTRACT OF THE DISCLOSURE A glueless interlock is provided in which two arms of a three-armed star cut in a box panel provide an insertion slot for a second panel or flap. The second panel or flap has an angular internal engagement slot in it, one arm of which coincides with one arm of the insertion slot. The other arm of the engagement slot may, but need not, coincide with the third arm of the star cut, but extends in the same general direction from the apex of the insertion slot as the direction of the third arm of the star cut from the star center. An intermediate apex portion of the engagement slot deviates from the course of the star out and outlines the base of a lock tip on the first panel at the star center which, in order to form a safety catch, may be snapped from the box inside past the apex portion to overlie the second panel beyond the area between the arms of the insertion slot.

The present invention provides improvements in glueless interlocks for folding box panels, such as corner locks or end wall locks, suited for high production rates at an exceedingly low rate of assembly failures, while maintaining extraordinary board economy.

The history of development of glueless interlocks extends over decades and provides an enormous variety of configurations.

Modern requirements for a superior lock are complex and varied. Details in the configuration of the lock affect the manner in which the box blank is cut, the manner in which the cutting and creasing die for the blank is built and the degree to which it remains within permissable tolerance in use, the manner in which excess material is stripped from a stack of blanks, the vulnerability of stripped blanks to damage, the behavior of a stack of blanks in a magazine, such as the susceptibility of blanks to interlock when being fed, the certainty with which the blanks are set up in box form, usually by a plunger-anddie type of device, the rate at which this can be accomplished (rates of 120 boxes per minute being not unusual), the ease with which formed boxes are removable from the setting-up device and, most importantly, the physical characteristics of the set up box. Among the latter there are such tests as: Is the lock vulnerable to accidental disengagement; do lock details interfere with the filling of boxes with tight fitting contents or the removal thereof; can the box structure serve as a box cover as readily as a box body; is the lock resistant to forces exerted during sealing of box cover flaps; is there objectionable bulk created at the corners which would interfere with the heat bonding thereto of a flat panel; and other tests.

A glueless interlock appears to involve, basically, no more than the configuration of edges, slots, and flaps, but a seemingly minor change in one or the other is likely to affect the production and the physical characteristics of the box in major respects, yet a seemingly favorable interlock construction, considering only the box aspect, may well be unfavorable from other aspects, for example from a production standpoint. The construction of a commercially superior interlock must therefore also be viewed 3,481,525 Patented Dec. 2, 1969 "ice at least in the light of all the mechanical devices involved in producing it.

The improved interlocks embodying the present invention employ a slot arrangement in the wall panel which, for the purpose of this specification, shall be referred to as a star cut, an arrangement of three cuts extending from a point, referred to as the star center, in three directions. Such star cuts are basically known and have been used in glueless interlocks in the past.

The panel or flap which is to be interlocked with the wall panel is inserted into an insertion slot formed in the wall panel by two of the three arms of the star cut and has formed in it an internally placed engagement slot of bent, angular or curved configuration, the essence being that one of the arms of the engagement slot is angularly disposed with respect to the other arm, there remaining an intermediate or apex portion between the arms which may be fiat, curved or otherwise shaped in such a manned that in the position of full insertion of the lock flap into the insertion slot the intermediate portion passes at some distance from the star center, thereby defining a lock tab portion on the wall panel whose tip may be snapped from an underlying position in a direction towards the box outside, past the edge formed by the intermediate portion, into a position overlying the lock flap. Thus snapped outwardly, the tab portion extends beyond the area of the lock flap between the arms of the engagement slot and acts as a safety catch which prevents disengagement of interlocking edges and withdrawal of the lock flap from the insertion slot.

A great number of advantages result. In the flat blank all interlocking portions or elements are interiorly disposed and not subject to damage during exterior stripping of the blank, transporting of blank stacks, and feeding. No blank portion bordering the star out or the engagement cut requires stripping to remove excess material.

The setting of the lock tip involves a displacement from the box inside towards the outside. Such displacement can be accomplished during that .stroke of the plunger which sets up the box by forcing the blank into a forming die. It is important that the setting of the tip need not await the end of the plunger stroke, but that it can be carried out during plunger travel and is completed by the time the plunger reaches the end of its stroke. No period of dwell is therefore required at the end of the stroke which, in turn, leads to smooth and rapid machine operation and permits high production rates.

The lock tip in its set position lies in the same plane as the wall portion bordering the insertion slot, therefore does not protrude, is protected from damage and does not catch on objects brushing past the box. Nor does it produce a high spot which would render more diificult the heat sealing of a cover flap placed thereover.

Efforts have been made in the past to create an interlock between a side wall and a corner flap by means of interiorly disposed slots provided in wall and flap.

According to one known proposal, vertical coinciding slots are provided in the wall and in the flap, respectively, and a split lug is formed within the medial portion of the wall slot which is then snapped past an edge of the flap slot, which at this point is also split. When being snapped into locking position the split lug must displace the split portion in the flap resulting in danger of the lug creasing at its base with consequent loss of rigidity of the lug on whose stifiness the security of the lock depends, as it is the only means of maintaining the slots in linear engagement.

Furthermore, the lug must be displaced against the resistance of a non-split portion of the flap which overlies it and offers considerable resistance to flexing.

If during assembly precise alignment of the slots is not obtained by reason of over-travel or under-travel of the flap with respect to the insertion slot, further complications arise.

In the event of under-travel of the flap no edge-to-edge engagement of the slots is obtained. In the event of overtravel (which is normally a desirable condition in order to insure engagement of the edges of the slots), the split tip of the lug encounters the non-split portion of the flap which then must be bowed out with considerable force in order to set the lug tip at all.

The present improvement employs a tab which is formed by the star cut in the wall panel and whose tip lies 'at the star center. This tab and tip are flexed outwardly against the sole resistance of a tab formed in the flap and readily yields to flexing. The tip, however, does not overlie the surface of the flexible flap tab in the engaged lock, but the unweakened, stiff flap area beyond the flap tab. This is accomplished by a corresponding orientation and arrangement of the engagement slot with respect to the arms of the star cut.

The objects, features and advantages of this invention will appear more fully from the detailed description which follows accompanied by drawings showing, for the purpose of illustration, preferred and representative embodiments of the invention, it being understood that in view of widely varying requirements for folding boxes for different contents and particular handling, no one specific form can properly be called the preferred embodiment.

The invention also resides in certain new and original features of construction and combination of elements and configurations herein set forth and claimed.

Although the characteristic features of this invention which are believed to be novel will be particularly pointed out in the claims appended hereto, the invention itself, its objects and advantages, and the manner in which it may be carried out, may be better understood by referring to the following description taken in connection with the accompanying drawings forming a part of the disclosure.

Certain of the figures will be referred to as combination box end elevational and blank plane views. These figures show a locked-up box corner at the left in elevation, and shown the blank portion for the right box corner at the right. The blank portion is shown in plan view and appears as if a portion of the box bottom and of the box side panel had been torn from the finished box and laid fiat.

FIGS. 1 and 3 are combination box end elevational and blank plan views employing locking elements of different configurations;

FIGS. 2 and 4 are elevational end views of the corresponding corners of the respective boxes as viewed from the inside of the box, bottom and side walls being shown in section;

FIGS. 5 to 13 are combination box end elevational and plan views employing locking elements of modified configurations;

FIGS. 14, 16 and 18 are plan views of blank portions for constructing interlocked box ends comprising an inner end flap and two partially overlapping end panels;

FIGS. 15, 17 and 19 are elevational end views of the respective interlocked box ends;

FIG. 20 is a plan view of another representative form of blank corner;

FIGS. 22, 24 and 26 are elevational end views of the box corner in three successive stages of interlocking;

FIGS. 21, 23 and are sections taken on lines 2121, 2323 and 2525 in FIGS. 22, 24 and 26, respectively; and

FIGS. 27 and 28 show modifications of the locking elements shown in FIGS. 7 and 12, respectively.

In the following description and in the claims various details will be identified by specific names for convenience. The names, however, are intended to be primarily descriptive and generic in their application. Corresponding reference characters refer to corresponding parts in the several figures of the drawings.

The drawings accompanying, and forming part of, this specification disclose certain specific details of construction for the purpose of explanation of broader aspects of the invention, but it should be understood that structural details may be modified without departure from the principles of the invention, and that the invention may be incorporated in other structural forms than shown.

Locking box corners Referring to FIGS. 1 and 2, the folding box A comprises a bottom panel 30 to which side panels 31 and an end panel 32 are articulated along side and end fold lines 33, 34, respectively. Corner or lock flaps 35 are articulated to the side panels 31 along corner fold lines 36.

Adjacent each corner the wall panel 32 has an in ternally disposed star cut S in it whose three arms 37, 38 and 39 meet at a common center point 40.

Each corner flap 35 has an equally internally disposed engagement slot E in it which comprises two arm portions 41 and 42 extending in different directions, there being an apex or intermediate portion 43 therebetween. In the illustrated example the apex 43 is pointed but, as will appear from the description of other forms, the apex portion may also assume a curved or fiat shape, which shall nevertheless be referred to as apex portion.

The assembly and interlock of the box corner proceeds in a basically known manner which involves the erection of the wall panels 31, 32 with respect to the bottom panel and the insertion of the corner flap 35 into the insertion slot.

This occurred in FIG. 2 and in the lefthand portion of FIG. 1. Only two arms of the star cut S, more particularly arms 37 and 38, are required to permit insertion of the corner flap and in a conventional manner.

The insertion slot 37, 38 is opened by flexing of the convexly bordered portion of the panel outwardly, so that the corner flap 35 can readily enter as it swings about the axis 33 during erection of the wall panel 31.

In the inserted end portion the arm 41 of the insertion slot moved slightly beyond the arm 38 of the star cut. This is theoretically not necessary, as movement of the two arms 41 and 38 into coincidence would be sufficient. The slight overtravel is nevertheless pratically desirable to make certain that even under unfavorable conditions of folding, or changes in the cutting and creasing die which produced the blank, the locking operation which will now be described is not impeded.

In order to set the lock, a force is locally applied at or near the X-mark shown in the drawings, the force being in the direction from the box inside to the box outside to force a portion of the panel 32 through the engagement slot, thus moving cut edges into engagement and forming a safety catch for such edge engagement.

The X-mark appears on a portion of the panel 32 which is concavely bordered by the star cut, more particularly arm 38 and represents a lock tab 44 within the panel 32, the tip of the lock tab lying at the star center 40.

When the corner flap 35 is first inserted the lock tab 44 lies entirely on the inside of the box and in the plane of the corner flap 35.

After application of the force which sets the lock, the tab tip snaps past the apex portion 43 of the engagement slot and then lies on the outside of the box substantially in the plane of the convexly bordered portion of the end panel 32. The portion of the corner flap 35 which is bordered by the engagement cuts 41 and 42 overlies the lock tab tip 44- which is thus protected in its safety-catch position against forces from the outside which might tend to disengage it, and against catching by parts brushing past the box end and even against the bottom edge of a telescoping box cover, should such a cover be placed over the tray-type box A.

In the position of full insertion of the corner flap 35, cut portions 39 of the star cut S and 42 of the engagement slot coincide.

Cut portions 41 and 38 may linearly coincide if so aligned, but normally intersect at a sharp angle causing the respective edges of cuts 38 and 41 to engage at about the point marked by the arrows L, if an outwardly directed force is exerted on the wall panel 31 by box contents, or otherwise.

As is quite evident from FIG. 2, box contents will not catch on any lock portions during insertion of the contents or their removal from the box.

The safety catch tip 44 does not add any bulk or protruding portion to the outside surface of the box end wall. This is of considerable importance in instances where another panel, for example a side or end flap of a hinge cover, is to be heat sealed to the box wall.

Considering the configuration of the blank by referring to the right hand portion of FIG. 1, it is apparent that all the critical portions of the interlock are internally disposed and are accordingly protected from damage during transport, stacking, storage and handling of the blanks.

The blank is free from protruding portions, such as tips or points, which would tend to interlock with the next blank in the stack and produce double feeding in automatic box erecting machinery.

It is further apparent that the lock setting force applied at the X marked portion and directed towards the box outside can be applied during the assembly operation during which a box forming plunger moves the blank through a forming die. By the time the plunger reaches the end of the stroke, the lock is set which presents a great advantage over locks which can only be set after the plunger has come to rest at the end of its stroke, thus requiring a moment of dwell which slows the assembly operation.

It will finally be observed that the tip of the lock tab 44 is spaced from the apex 43 of the engagement slot. This is a common characteristic of the various lock forms disclosed herein.

The advantages of the lock configuration of FIGS. 1 and 2 are also found in the modifications of the subsequent figures which for this reason require only a brief description and mention of their specific features.

In the lock configuration of FIGS. 3 and 4 the two portions 337 and 338 of the star cut which form the insertion slot are aligned and an edge-to-edge engagement of considerable length is brought about between the edges of cuts 339 and 342. The lock tip is downwardly directed and the apex portion 343 of the engagement slot is fiat. An additional edge-to-edge engagement is brought about between edges of cuts 337 and 341.

The resulting box corner is very strong and can be set up on a particularly simple form of plunger-and-die device in which no back up elements, such as pressure rollers or bars, are required on the die in order to counter the lock setting force applied at X, but in which a blade element on the plunger performs the countering operation as will later be described in connection with FIGS. 21 to 26.

In the locked corner the tip 344 which forms the safety catch lies protected below the level of the corner flap by a distance equal to the thickness of the board. The tip is visible from the outside adjacent the apex edge 343 and has the shape of a triangle.

Viewing the locked corner from the box inside (FIG. 4) the apex edge 343 is visible, but the triangular tip portion, which prior to the setting of the lock lay immediately above the star cut center 340, is not visible, as it was snapped past edge 343 to the outside.

It is a known phenomenon that crease scores may break along one side of the crease, or along the other side of the crease or approximately down the center of the crease. Assuming that in the upfolding of the wall panel 6 531 in FIG. 5 the score 533 breaks on the bottom panel side, the effect will be a slight raising of the corner flap 535 with respect to the star out 537, 538, 539.

Assuming that in the inserted position the engagement slot portion is horizontally disposed, a problem might then arise as the lock tip 544 might not clear the raised edge of slot 542.

In order to avoid this danger, the slot portion 542 is slanted downwardly with the effect that any possible interference caused by the raising of the lock flap will occur only at or near the apex portion 543 where the lock tip 544 must, in any case, be snapped past an obstructing edge, the edge formed by the apex portion 543.

The modification shown in FIG. 5 thus disposes of the danger created by a raised lock flap, at a relatively slight sacrifice, namely that no linear edge-to-edge engagement occurs between edges 539 and 542. Engagement edge 541 nevertheless engages fully with the vertical portion of the arm 537 of the star cut, and such engagement is sufficiently strong and rigid for most purposes.

The interlock configuration of FIG. 6 is inherently immune to elfects of raising of the lock flap 635. If the portion 642 of the engagement slot is raised with respect to the arm 639 of the star cut, the clearance for the lower edge of the cut portion 639 is increased and the displacement of the tip 644 past the apex 643 is not rendered more ditficult. The overlap of the tip 644 with respect to the apex portion 643 decreases slightly in such a case, but sufficient overlap can be insured by making the portion 643 long enough. Edge 641 engages edge 638 along a substantial length and the consequent resistance to disengagement of the lock is great.

The interlock configuration of FIG. 7 comprises an engagement slot having a pointed apex 743. The tip 744 of the lock tab is likewise pointed and the tip 744 overlaps because of the difference in angular disposition of cuts 739 and 742.

An advantage of the design of FIG. 7 over that of FIG. 6 is that, in a box subject to compression from the outside, the panel 732 is less likely to buckle above the T-shaped star cut, as theslanted head bar of the T provides more bulk of board between cut 739 and the top edge of the wall 732.

In the interlock configuration of FIG. 8 the engagement slot is arcuate and arms 841, 842 and apex portion 843 are portions of the same are whose curvature, however, need not be uniform from end to end.

The engaged and set interlock is shown at the left of the figure. The inter-engagement of the cut edges is of the point-to-point type and occurs approximately at the point marked by arrows L.

The star cut of the interlock configuration of FIG. 9 may be termed a slanted T and the engagement slot is a flat bottom V which is upright in the assembled box. The lock tip is downwardly directed and is exposed below the substantially horizontal apex portion 943. In that position the tip underlies the V-shaped area of the lock fiat! 935 which is bounded by the engagement slot 941, 942, 943, this area being slightly flexed outwardly. The tip 944 overlies the flap 935 just beyond the apex portion 943 and lies in substantially the same plane as the adjacent portion of the wall panel 932. This provides protection of the tip against damage. The box inside is completely free from protruding tips and points, and pressure of box contents on the lock from the inside, for example if a box were filled with small screws, produces no tendency to disengage the lock.

In cases where the triangular wall portion bordered by star arms 937 and 938 is objectionable for the reason that this portion is a point aimed at the corner fold line 936, the modification of FIG. 10 removes such objection.

In the configuration of FIG. 10 the corresponding wall portion is of obtuse angularity due to the shaping of the star cut in the form of an upright Y. The apex portion 1043'is shown curved rather than fiat, this being optional.

The curved configuration permits use of a single appropriately curved knife in the cutting and creasing die for the blank. The arm 1037 of the Y is angled off horizontally to provide a strip of board of adequate width between the top of the Y and the top edge of the box.

The interlock of FIG. 11 produces a linear edge-to-edge engagement of edges of cuts 1141 and 1138. In the position of full insertion of the corner flap 1135 in the insertion slot 1138, 1137, the face of the wall panel 1131 abuts the side edge of the wall panel. The setting of the lock tip 1144 may provide ditficulties unless the edge of star out arm 1138 has sufficient clearance to pass the edge of the engagement slot 1141. In order to assure such clearance a slight amount of over-travel of the corner flap is preferably provided, so as to move slot 1141 slightly beyond star out arm 1138. This is indicated in the left hand portion of FIG. 11 by a dotted line.

The same basic idea of over-travel is incorporated in the interlock configuration of FIG. 12. In the fully inserted position the slot portion 1241 intersects the star cut arm 1238 at an acute angle thereby providing sufficient clearance near the apex 1243 for the lock tip 1244. Ample clearance also exists for the bordering edge 1239 of the tip by reason of the upward slant of slot 1242.

Upward displacement of the lock flap 1335 by reason of breaking of the side panel fold line 1333 closer to panel 1330 than to panel 1331 does not produce any difficulties in the design shown in FIG. 13. In view of the upward slant of the engagement slot arm 1342 the lock tip 1344 moves to a position of increased overlap with respect to the corner flap 1335, but no clearance problems arise at slot 1342.

Locking box end panels The interlocking of partially overlapping end panels of a folding box involves not only all the problems encountered in locking a box corner, but also a further problem, the prevention of parallel vertical displacement of the end panels manifested, for example, by one panel moving into a higher or lower position with respect to the other panel. Such motion is likely to occur as a result of racking of the box, which is the rotational twisting of one box end with respect to the other.

Vertical displacement of the end panels must be avoided not only by reason that it permits the box to assume a misshapen form, but also for the reason that safety catches of a glueless end wall interlock may become disengaged.

FIGURES 14 and 21 illustrate the adaptability of certain previously described elements to the interlocking of box end panels.

In FIG. 14 so much of a box blank is shown as is required to construct a box end comprising an inner end panel and two outer partially overlapping end panels.

A bottom panel has side wall panels 51 and 52 articulated to its along bottom side fold lines 53 and 54. An inner end panel 55 is articulated to the bottom panel along an end fold line 56 and a first and a second outer end panel 57, 58 are articulated to the side panels 51 and 52 along corner fold lines 59 and 60, respectively.

A hook 61 is formed on the second outer end panel which is pointed towards the bottom panel after assembly of the box end, and a shoulder 62 is formed above the hook. Such hook-and-shoulder configuration is known in box end construction of this general type.

The first outer end panel 57 has a star cut formed in its comprising arms 63, 64 and 65 extending from the star center 66. The far end of the arm 64 is returned at 67, the return having a small radius, this being a configuration preferable over a straight end for reasons which will presently appear.

An engagement slot is formed in the second end panel and comprises arms 68, 69 and an apex portion 70.

The assembled box end is shown in FIG. 15. The inner end panel 55 is folded upright with respect to the bottom panel 50, the end panels 57, 58 are folded thereover, and the hook 61 is inserted into the slot which opens by defiecting the board slightly adajacent star out arms 64, 63. The notch 71 of the hook 61 seals on the return 67 and the shoulder 62 engages the end of star out arm 63. The hook-and-shoulder engagement prevents vertical displacement of end panels 57 and 58 in a known manner, but the interlock is still vulnerable to forces tending to pull the panels apart horizontally.

In order to render the lock secure in that direction, a lock setting force is applied to the X mark which snaps the lock tip 72 past the apex portion 70 of the engagement slot and produces an edge-to-edge engagement between the engagement slot portion 68 and star cut arm 64. As in previously described forms of the interlock, the tip 72 is protected, as it lies by one board thickness below the face of that portion of the panel 57 which lies adjacent to cut 64 opposite the X mark.

Setting of the lock tip is possible from the inside as the upper edge of the inner end panel 55 terminates below the X marked portion of panel 57.

The blank of FIG. 16 incorporates a lock configuration which locks the outer end panels against horizontal as well as vertical displacement without the use of a shoulder configuration above the hook. In order to avoid the need for a detailed description of the various elements, reference numerals are used which differ from those of FIG. 14 by 100.

The assembled and locked up box end is shown in FIG. 17. The hook 161, 171 limits movement of panel 158 relatively to panel 157 in a downward direction. Edge-to-edge engagement between star arm and engagement slot arm 169 prevents movement of the panel 158 relatively to panel 157 in an upward direction. The panels are locked against being pulled apart horizontally, firstly by the hook 161 engaging at its notch 171 the cut return 167 and, secondly, by engagement of the upper portion of star cut 164 by engagement-slot arm 168. Snapping of the tip 172 past the concave edge of the engagement slot apex 170 secures the lock.

In the modification shown in FIGS. 18 and 19 parts and elements are identified by numerals differing from those used in FIGS. 14 and 15 by 200. No shoulder is provided on end wall panel 258. Snapping of the lock tip 272 prevents vertical upward motion of panel 258 with respect to panel 257, as such movement is resisted by the engagement of two pairs of edges 268, 264 on the left and edges 269, 265 on the right.

Setting the lock When setting the lock by pressing the tip 44, 144, 244, etc. of the lock tab past the edge in the lock flap which is formed by the engagement slot, it is of course necessary to provide for adequate backing of the edge against the force exerted on the X marked portion.

Such backing may in a plunger-and-die device be provided by a roller on a bar past which the respective box portion moves on its travel through the die.

Certain lock forms, as represented for example by FIG. 3, may be set without backing-up of any box portion by the die, as the backing-up may be done from the box inside by the forming plunger. For this purpose the latter is equipped with a multiple purpose element which will now be described by reference to FIGS. 20 to 26 showing in FIGS. 21 to 26 successive phases of operation performed on the blank.

FIG. 20 illustrates a representative lock configuration which may be regarded as a modification of the lock of FIG. 3. Its details are sufficiently identified by the application of reference numerals identical in the last two digits with those used in FIG. 3.

An axially reciprocable pin 73 (see also FIG. 21) bears against the lock tab, whose tip is 2044, at a location marked in other figures by an X-mark. This pin would be mounted on the forming plunger about which the blank is folded in order to set up the box.

A countering force is provided by a blade 74 mounted on a stem 75, stern and blade being rigidly carried by the plunger. 1

FIGS. 21 and 22 illustrate the first phase of the comer forming operation. The blade bears against the inside surface of the side wall panel 2032 causing it to bulge out slightly, thereby opening the insertion slot 2038 through which the lock flap 2035 enters. In its fully inserted position the lock flap 2035 lies on the inside face of the blade 74 while the wall panel 2032 bears against the outside face. The pin 73 is fully retracted during the first phase.

The lock setting operation is illustrated in FIGS. 23 and 24. During the second phase of operation the pin 73 is projected as indicated by arrow 76 and pushes the lock tip 2044 past the edge of the insertion slot of the lock flap 2035 at the apex portion. During this phase that portion of the corner flap which appearsin FIG. 23 below, and slightly to the right of the center line of the pin 73, is backed up by the blade 74. The tip 2044 now lies on the outside of the corner flap 2035.

The pin then retracts, as indicated by arrow 77, and the several panels settle to the position shown in FIG. 25. The assembly is still bulged out slightly due to the presence of the blade 74.

This is the position of the box elements, and of the pin 73 and blade 74 at the end of the stroke of the box forming plunger. Assuming now that the box is arrested, for example by a strip oif catch 78 engaging the upper box edge, the plunger can be withdrawn in an upward direction causing the blade to slip out from between the corner flap 2035 and the wall panel 2032.

It is clearly apparent that there is no portion of the star cut or any other edge which obstructs, or interferes with, the withdrawal of the blade 74 which performed two functions, the function of opening the insertion slot 2038 and the function of backing up the corner flap during the setting of the lock tip 2044.

The design of the plunger and die forms the subject matter of a separate copending patent application Ser. No. 749,759, filed Aug. 2, 1968.

The corner lock designs shown in FIGS. 27 and 28 may be considered modifications of the locks of FIGS. 7 and 12, respectively.

Details and elements of the design of FIG. 27 are identified by reference numerals differing from the numerals used in FIG. 7 by 1000.

Following the outline of the upright arm 1738 of the star cut, an angular offset 78 is provided at a short distance from the star center 1740. The offset results in the formation of a blunt tip on the lock tab 1744.

In the assembled lock shown at the left in the figure the portion 1741 of the engagement slot in the flap 1735 lies in coincidence with the lower portion of the arm 1738 of the star cut which forms a portion of the engagement slot. The upper offset portion of the arm of the star cut is out of coincidence with the portion of the engagement slot 1741 adjacent the apex 1743.

An outwardly directed force applied at the X mark forces the lock tab 1744 past the edge of the engagement slot portion 1741 and the blunt square tipped tab 1744 overlies the corner flap and fits again into the angular cutout produced in the wall panel 1732 by the offset 78. In this position the tip is protected and does not protrude from the surface of the box wall.

In the design of FIG. 28 the arm 2239 of the star out is angled off at a distance from the star center 2240, the angled off position being designated 2239'. Again, a blunt-nosed tab 2244 results which is snapped into locking positioning by a force applied at the X mark.

As seen at the left, the tip 2244 overlies the corner flap 2235 adjacent the engagement slot portion 2241 and lies adjacent the upwardly slanting edge of the star cut arm 2237.

An advantage of a blunt tipped lock tab design is that the overlapping area of the tip is enlarged, thereby insuring that the safety catch is always more than marginal in size.

What is claimed is:

1. An interlock for two corner-forming wall panels of a folding box, one of the wall panels having a flap articulated to it at a corner fold line, said flap being foldable over, and insertable into an insertion slot in, the other wall panel in which the insertion slot is formed by two arms of a three-armed star cut, and in which the flap has an internally disposed slot in it comprising a first arm portion, a second arm portion extending in a direction differing from the direction of the first arm portion and an apex therebetween, said first arm portion coinciding with one of the two arms of the insertion slot, the two arm portions defining a flap tab between them, and said apex, in the condition of full insertion of the flap in the insertion slot, being spaced from the star center, thus defining on the wall panel a wall tab area, the tip of which lies at the star center, characterized in that in inserted position the second arm portion of the flap slot extends from the apex in the same general direction as the third arm of the star cut extends from the star center thus causing the flap tab and the wall tab to point in substantially the same direction, the tip of the wall tab being forceable from an underlying position with respect to said flap past an edge of the flap slot into an overlying position.

2. An interlock for two corner-forming wall panels of a folding box, one of the wall panels having a flap articulated to it at a corner fold line, said flap being foldable over, and insertable into an insertion slot in, the other wall panel in which the insertion slot is formed by two arms of a three-armed star cut, and in which the flap has an internal angular slot in it comprising an apex portion and a first and a second arm portion extending from the apex portion in different directions, said arm portion bordering a flap tab of which the apex portion is the tab point, said first arm portion coinciding, at least partially, with one of the two arms of the insertion slot and said tab point, in the condition of full insertion of the flap in the insertion slot, being spaced from the star center thus defining in the wall panel a wall tab, the tip of which lies at the star center, characterized in that in inserted position the second arm portion of the flap slot extends from the apex in the same general direction as the third arm of the star cut extends from the star center thus causing the flap tab and the wall tab to point in substantially the same direction, the tip of the wall tab being forceable in a direction towards the outside of the box past an edge of the flap slot into a position overlying the lock flap and extending over a flap area outside the confines of the flap tab.

3. A folding box structure as defined in claim 1 in which said second arm portion coincides with at least a portion of the third arm of the star cut.

4. A folding box structure as defined in claim 1 in which the internal flap slot is of arcuate shape.

5. A folding box structure as defined in claim 1 in which the star cut is substantially in the form of a T, the stem of which is upright with respect to the main panel of the box and in which the first arm portion of the flap slot coincides with said stem.

6. A folding box structure as defined in claim 5 in which, further, the second arm portion of the flap slot coincides with at least a portion of the third arm of the star cut.

7. A folding box structure as defined in claim 1 in which the star cut is substantially in the form of a T, the head bar of the T being substantially upright with respect to the main panel of the box, in which one of the arm portions of the flap slot coincides with at least a portion of the head bar of the T, and in which the end of the head bar of the T which is remote from the main panel is angled off.

8. A folding box structure as defined in claim 7 in which the other arm portion of the flap slot coincides with at least a portion of the stem of the T.

9. A folding box structure as defined in claim 1 in which the star cut is substantially in the form of a Y.

10. A folding box structure as defined in claim 9 in which the Y is substantially upright with respect to the main panel of the box.

11. A folding box structure as defined in claim 9 in which the Y is substantially upright with respect to the main panel of the box and in which the portion of the stem of the Y which is adjacent the main panel is angled oil? in a direction away from the box corner.

12. A folding box structure as defined in claim 1 in which the star out is substantially in the form of a T so oriented that the stem of the T is directed generally away from the corner point, in which orientation the head of the T is closest to the corner point, and in which the flap slot is substantially in the form of a flat bottomed V.

13. A folding box structure as defined in claim 1 in which the star cut is substantially in the form of a T so oriented that the stem of the T is substantially upright with respect to the main panel and in which the angle defined by the arms of the flap slot is larger than the angle defined by the arm portions of the star out which underlies the flap slot.

14. In a folding box comprising two wall panels forming a corner, one of the wall panels having a flap articulated to it at a corner fold line, said flap being foldable over, and insertable intoan insertion slot in, the other wall panel in which the insertion slot is formed by two arms of a three-armed star cut, and in which the flap has an angular internal slot in it comprising a first arm portion, a second arm portion extending in a direction differing from the direction of the first arm portion and an apex portion therebetween, said first arm portion coinciding with one of the two arms of the insertion slot, the two arm portions defining a flap tap between them, characterized in that said apex portion defines, in the condition of full insertion of the flap in the insertion slot, the base of a tip on the wall panel tab, which tip lies at the star center and may be forced from an underlying position with respect to said flap past the apex portion of the flap slot into a position overlying the lock flap in an area outside the said flap tab.

15. An interlock for interconnecting two panels of a paperboard structure in which a portion of one panel is inserted into an insertion slot in the other panel and in which the insertion slot in said other panel is formed by two arms of a three-armed star out and in which the one panel has an internal angular engagement slot in it, at least a portion of a first arm of which, in the condition of full insertion of the said one panel portion, coincides with one of the insertion-slot-forming arms of the star cut, a second arm of the engagement slot extending at an angle to said first arm, the two arms of the engagement slot defining a first tab, there being an apex between said first and second arms, which apex is offset with respect to the center of the star cut and outlines the tip of a second tab formed in said other panel, said tip lying at the star center, characterized in that in inserted position the second arm portion of the engagement slot extends from the apex in the same general direction as the third arm of the star cut extends from the star center, thus causing said first and second tab to point in substantially the same direction, said tip of the second tab being forceable from an underlying position with respect to said one panel past an edge of the insertion slot into an overlying position with respect to said one panel into a position beyond the confines of said first tab.

16. An interlock as defined in claim in which the apex angle of the engagement slot is larger than the angle defined by the arm portions of the star cut which underlie the engagement slot.

17. An interlock as defined in claim 15 in which the engagement slot is of arcuate shape.

18. An interlock as defined in claim 15 in which the second arm of the engagement slot coincides with at least a portion of the third arm of the star cut.

19. An interlock as defined in claim 15' in which the two wall panels are flaps extending from opposite wall panels of the paperbox structure, and in which the one panel has at least one abutment portion formed thereon which engages an end of the insertion slot to limit relative movement of the panels in a direction substantially parallel to the corner fold lines.

20. An interlock as defined in claim 19 in which one panel has a first abutment formed thereon engaging the end of the arm of the star cut which extends substantially parallel to the corner fold lines and has a second abutment formed thereon in the form of a shoulder engaging the end of the second arm of the star cut, which second arm forms a part of the insertion slot.

21. An interlock as defined in claim 19 in which the open panel has an abutment formed thereon in the form of a hook engaging that end of the arm of the star cut which extends substantially parallel to the corner fold lines, in which one arm of the engagement slot is in coincidence with at least a portion of the star out arm last referred to, and in which the other arm of the engagement slot coincides with at least a portion of the third arm of the star cut, the tip of the lock tab pointing in substantially the same direction as the hook.

22. In a folding box comprising two wall panels forming a corner, one of the wall panels having a flap articulated to it at a corner fold line, said flap being foldable over, and insertable into an insertion slot in, the other wall panel in which the insertion slot is formed by two arms of a three-armed star cut, the improvement which is characterized in that the flap has an internally disposed angular slot in it comprising a first arm portion, a second arm portion extending in a direction differing from the direction of the first arm portion and an apex therebetween, said first arm portion coinciding, at least partially, with one of the two arms of the insertion slot and said apex, in the condition of full insertion of the flap in the insertion slot, being spaced from the star center, the portion of said second arm portion which lies adjacent the apex being out of coincidence with the star out thereby defining on the wall panel a lock tab area, the tip of which lies at the star center and may be forced from an underlying position with respect to said flap past an edge of the flap s ot into an overlying position.

23. A folding box structure as defined in claim 22 in which the tip of the lock tab is blunt.

24. A folding box structure as defined in claim 22 in which the star cut portion which forms the lock tab is angled off at a distance from the star center, thereby producing a blunt lock tab tip lying between the star center and said angled oif portion.

References Cited UNITED STATES PATENTS 1,515,983 11/1924 Williams 22935 1,842,755 1/1932 Hill 22935 2,677,493 5/1954 Wauda 22935 3,112,854 12/1963 Persson 22939 377,813 2/1888 Munson 22935 1,680,661 8/1928 Birrell 22935 2,605,955 8/1952 Meller 22935 3,053,429 9/1962 Pierce 22932 3,285,494 ll/1966 Baker 229-36 DAVID M. BOCKENEK, Primary Examiner US. Cl. X.R. 22932, 36 

